1. Technical Field
The present invention relates to an on-board network system comprising a plurality of electronic control units that are communicably connected with each other over a communication bus to share control messages accompanying control of on-board devices mounted in a vehicle, and providing a network management function.
2. Description of the Related Art
Conventionally, numerous electronic control units (ECUs) are mounted in a vehicle to control on-board devices. An on-board network system includes the ECUs being disposed on a communication bus.
In an on-board network system such as this, each ECU transmits control messages to the communication bus. The control messages include various detection values indicating the state of the vehicle, commands issued to the on-board devices, and the like. The control messages are shared among other ECUs, thereby actualizing efficient and comprehensive vehicle control.
In addition, in the on-board network system, a network management (NM) function is being reinforced in accompaniment with the increase in the number of ECUs mounted in the vehicle. Here, the NM function is provided to manage whether nor not each ECU is operating normally. The operations of the ECU include a so-called bus-sleep operation. In the bus-sleep operation, when control messages are not required to be transmitted and received over the communication bus, each ECU transitions, for example, its own communication controller and transceiver to power-saving mode, thereby transitioning from a “normal state” to a “power-saving state”, to suppress power consumption of the overall system.
In addition, as a working of the bus-sleep operation, a situation is known in which, in the normal state, each ECU periodically transmits a network management (NM) message indicating that transition to the power-saving state is not possible. When transition to the power-saving state becomes possible, the ECU ceases transmission of the NM message. In addition, when the NM messages from other ECUs are no longer received, the ECU transitions from the normal state to the power-saving state.
In other words, when each ECU is no longer required to use the communication bus for itself and is no longer required to use the communication bus for the other ECUs, control messages are no longer required to be transmitted and received. Therefore, the ECU transitions from the normal state to the power-saving state. In some instances, in addition to the communication controller and transceiver of the ECU entering power-saving mode, power supply to the microcomputer of the ECU may also be stop. Power supply to the microcomputer being stopped in this way is referred to as microcomputer-sleep.
In this type of on-board network system, a system is known in which an ECU (relay device) that relays the transmission and reception of control messages between a plurality of communication buses monitors the operating state of other ECUs (nodes). Depending on whether the node that is the transmission source is in the normal state or the power-saving state, the ECU (relay device) relays or stops relaying the NM messages (for example, refer to JP-A-2011-87112).
However, in the conventional on-board network system, the operating state of a node is judged only based on whether or not the NM message has been received. Therefore, a problem occurs in that it cannot be determined whether the node has ceased transmitting the NM message because of a normal operation or is unable to transmit the NM message because of some sort of malfunction (abnormality). In other words, in the latter instance, a problem occurs in that the abnormal operation of the node cannot be favorably detected in the NM function.
Therefore, an on-board network system providing an NM function is desired that is capable of efficiently detecting operation abnormality in the system.